We propose to conduct a randomized, double-blind, placebo controlled clinical trial of the efficacy of beta carotene as a chemopreventive agent for non-melanoma skin cancer. This is a collaborative investigation to be conducted at four study centers with a central data coordinating center. We anticipate a total study population of 1,950. Eligible subjects will be recruited from the four participating institutions by being identified from records of dermatology services and pathology laboratories as having a proven diagnosis by biopsy of either basal or squamous cell carcinoma of the skin during the previous two years or by presenting for treatment of a non-melanoma skin cancer during the first year of the study. The study participants will take either 30 mg. of beta carotene or 30 mg. of placebo every day. Each subject will have a total skin examination yearly with biopsy of all suspicious lesions. Serial sections of all lesions will be reviewed centrally according to a uniform protocol. Blood for carotene and retinol analysis will be drawn on a subset and sent to a central laboratory for analysis. Each year participants will complete a questionnaire providing information on compliance with the drug regimen, possible drug side effects experienced and non-dermatological diseases occurring over the yearly interval.